There have been many efforts over time to use local power sources to supplement energy requirements from a utility power grid. Common examples include solar cells with photovoltaic (PV) inverters. Other examples may use wind energy, or another naturally occurring source, such as geothermal energy. Such sources are used in tandem with power drawn from a traditional power grid in the hope of reducing the power (and consequent cost) drawn from the grid. Such systems are designed to deliver power from the source to a load that includes both the local load and the power grid. Thus, from the perspective of the local source looking out, traditional designs lump the local load and the grid as the target for power delivery from the system. Therefore, in practice such systems have always supplied both real and reactive power to the local load.
The power transfer from the local source to the local load is typically inefficient, resulting in the user wasting energy generated locally, which is then drawn from the grid. Thus, even where a local source may generate significant amounts of energy that would seemingly satisfy the needs of the local load, the local load typically must also draw real and reactive power from the grid at measurable cost to the customer.
The tariff governing the cost of electricity to utility power grid customers depends upon many factors, including size of a customer's base load, the time of day that the electricity is demanded, and the type of power demanded (whether it be active or reactive power). The tariff structure requires the customer to pay more, for example, if the power is used during peak demand hours, when the utility has little reserve available for emergencies, or, for example, if the type of power is active, instead of reactive power. In general, residential customers do not pay for reactive power under current tariffs, whereas industrial customers do.
Reactive power is becoming more costly to the utilities to produce than it once was, for several reasons. First, the demand for reactive power is growing much faster than for active power, because many new electronic and electrical products are requiring more reactive power than ever before. These products include plasma and LCD TVs, computer power supplies, and grid-tie electrical vehicles. Second, reactive power is more costly to transport down long distance transmission lines than is active power, because it causes voltage drops approximately 10 times greater than does active power. Third, although reactive power can be compensated for on the local distribution lines, thereby canceling the need to build larger generating stations many kilometers away, the compensators are expensive to buy and maintain.
Descriptions of certain details and implementations follow, including a description of the figures, which may depict some or all of the embodiments described below, as well as discussing other potential embodiments or implementations of the inventive concepts presented herein. An overview of embodiments of the invention is provided below, followed by a more detailed description with reference to the drawings.